The present invention relates to a device for ameliorating RF radiation, and in particular to such a device which is attachable to a cellular telephone so as to minimize the absorption of RF radiation by persons using the telephone. The term "ameliorating" is used herein to mean "reducing".
Recently, there has been considerable concern that the use of mobile communication devices may cause health problems in those persons using the devices. In particular, there has been concern that the widespread use of cellular telephones may stimulate the growth of tumors in areas of the human brain which are in the proximity of the cellular telephone's antenna. C. M. Fischetti, "The Cellular Phone Scare" IEEE spectrum, June 1993, pages 43-47. Scientists and others believe that the radiation emitted by the cellular phones may eventually cause significant health risks as the use of cellular phones becomes more and more common. In particular, there is concern that when the telephone is placed close to the head, power deposition from the transceiver and antenna may cause thermal insult on the brain and other organs of the head. Power deposition is typically quantified by the specific energy absorption rate, commonly referred to as SAR.
In light of these concerns, the governments of several countries have implemented restrictions on exposure to high frequency electromagnetic fields in terms of localized SAR. See IEEE C95.1, 1991, IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, and Mckinley et al., Restrictions on Human Exposure to Static and Time Varying Electromagnetic fields and Radiation, Documents of the National Radiological Protection Board, 4 (1993). These concerns are especially heightened in view of proposals being considered in a number of countries to raise the frequencies at which cellular phones may communicate. Higher frequencies are considered to pose even a greater threat.
While these restrictions place maximum limits on SAR, there is currently insufficient knowledge about the effect of low levels of RF radiation to determine whether long-term, low-level exposure can be harmful. Thus, several antenna shields have been developed for further reducing the amount of RF radiation received by the user. Typically, such shields extend from the cellular phone in a manner so as to be generally parallel with the antenna and positioned between the antenna and the head of the user. While such shields do reduce the amount of RF radiation received by the user, they have several problems. First, the shields are generally non-collapsible. While most of the new cellular telephones have collapsible antenna, the shield extends several inches from the telephone, even when the telephone is not in use. Thus, the advantage of retracting the antenna is lost and more storage space is needed.
Another disadvantage of the antenna shields is that they significantly reduce the range of the cellular phone. By interfering with the RF radiation emitted by the antenna, the shield causes a loss in range by a factor of 2 to 3 in an urban environment. Furthermore, the shield has a tendency to redirect the RF radiation away from the user and back into the telephone, potentially shortening the life of the telephone.
To alleviate the potential health risks, while not significantly interfering with the telephone's functioning, there is a need for a device which decreases the RF radiation received from cellular telephone, without disturbing the RF radiation emitted from the telephone.